Generally, a prosthetic heart valve is used as a surgical replacement for a person's heart valve if it is damaged or has a functional deficiency. It is also used to prevent reverse blood flow in recently developed prosthetic hearts or ventricular assist devices.
Prosthetic heart valves may be divided into mechanical valves, tissue valves, and polymer valves according to the main material used, where a mechanical valve uses a circular or semicircular hinge flap with its movement restricted to one direction to prevent reverse blood flow, and a tissue valve includes the heart valve or the pericardium surrounding the heart of an animal fabricated into a structure similar to that of the aortic valve or pulmonic valve of the heart. A polymer valve uses medical-grade polymers that are molded into a form similar to the aortic valve or are fabricated into a structure that serves as a unidirectional check valve.
Here, the structure of an aortic valve or a pulmonic valve includes three flexible membranes for preventing reverse blood flow, and hence is referred to as a trilobate valve, and existing tissue valves and polymer valves are usually fabricated in a form similar to this.
Furthermore, since the leaflets of a prosthetic heart valve must possess a flexible quality similar to the leaflets of a biological heart valve and must operate within the body for an extended period of time without irregularity, durability is an important criterion in selecting the material. Also, since there is direct contact with blood, a material having good compatibility with blood must be chosen or a material that has been imbued with compatibility with blood must be used.
The existing method of manufacturing such a trilobate polymer valve includes two steps. First, the part corresponding to the leaflets is first fabricated.
This process entails fabricating molds having a form similar to that of the leaflets, repeating the processes of immersing the molds into a polymer solution and drying, and separating the polymer membranes from the molds to form leaflet shapes. Next, a valve conduit for surrounding the fabricated leaflets may have three leaflets attached therein to complete the process. Here, it is advantageous to form a sinus for each leaflet within the valve conduit in order to minimize regions where the blood remains stagnant when the valve is closed, the thickness may be two to twenty times thicker compared to the leaflets when considering the thickness of the aorta within the body, and the strength should be of a level that is sufficient for use within the body.
The existing process of manufacturing a trilobate polymer valve such as that described above requires providing the polymer in a solution state and fabricating the valve conduit separately by injection molding or a different method before attaching the components. The time required for production was several days, the level of quality was not consistent due to the manual labor involved in the immersing and attaching processes, and the usefulness was low because of the low productivity.
As an effort to resolve these problems, the stent valve of Patent Document 1 was proposed.
The stent valve according to the related art mentioned above includes: (a) a single radial expanding vessel stent that has a diameter, a proximal end, and a distal end; and (b) a valve that has a valve proximal end and a valve distal end, is at least partially positioned inside the stent, and forms a valve opening by means of the valve proximal end being arranged at the proximal end of the stent, wherein the valve includes at least two pocket structures for blocking the flow of blood, the pocket structures are positioned within the stent, the pocket structures include flexible portions that cooperate to form a valve opening adjacent to the proximal end of the stent, the flexible portions include outer portions that connect to the stent and extend inwards from the stent to form the valve opening, each of the pocket structures includes a layer that extends from the apex of the pocket structure to towards the proximal end of the stent, the layer is sutured to the inside of the stent to cover the inside, and the apex of the pocket structure is positioned adjacent to the distal end of the stent.
However, the stent valve according to the related art described above, where two pocket structures are inserted into and connected within the vessel stent to perform the function of a valve and operate such that blood may flow towards the heart but may not move out of the heart, is vulnerable to the problem of tearing due to prolonged use at the portion where the vessel stent and the pocket structures are connected as well as the problem of the valve losing its functionality when the elasticity of the pocket structures is lost.
Also proposed were the stent-valve for valve replacement and associated methods and systems for surgery of Patent Document 2.
The valve according to the related art mentioned above includes a valve component; and a stent component that includes a first section, a second section for housing the valve component, and a third section, where the first section includes an annular groove.
However, the valve according to the related art described above is manufactured in the form of an integrated body, so that not only may the manufacturing procedure be complicated and the manufacturing costs be increased, but also tearing may occur at the connecting portions when it is used coupled to a wire stent.
Also proposed was the cardiac valve prosthesis for replacement of the aortic valve of Patent Document 3.
The valve according to the related art mentioned above is made from a bovine pericardium and is formed by an inner sheet having three semicircular portions and an outer sheet made from the bovine pericardium, with the inner sheet and the outer sheet sutured together, rolled into a cylindrical shape, and sutured at both ends.
However, the valve according to the related art described above entails the problem of tearing occurring at the connecting portions when it is used coupled to a separate wire stent.
Also proposed was the prosthetic heart valve of Patent Document 4.
The valve according to the related art mentioned above includes a plurality of thin, flexible leaflets, each of the leaflets having an inner face, an outer face, an inflow edge, an out-flow edge, and side edges, the plurality of leaflets being sewn together along at least a portion of their side edges so as to form a substantially tubular valve structure having an in-flow end and an out-flow end, adjacent leaflets being arranged so that their side edges are substantially aligned and the inner faces of the leaflets engage each other adjacent the side edges, whereby the valve structure is movable between a closed position in which the out-flow edges of adjacent leaflets engage each other, and an open position in which the out-flow edges of adjacent leaflets are separated from each other except along the side edges, and the sewn portions of the side edges of the leaflets bias the leaflets toward a partially closed position.
However, with the valve according to the related art described above, the sewing required for the manufacture of the cylindrical shape results in the sewn portions protruding outwards, which may leave gaps between the sewn portions and the inner cavity of an artery during a surgical procedure or may make connection difficult when the valve is used coupled with a separate wire stent.